In the fabrication processes for a semiconductor device, numerous processing steps must be carried out on a semi-conducting substrate before the device is fabricated. The numerous processes may be as many as several hundred processing steps. Each processing step is executed in a process chamber such as an etcher, a physical vapor deposition chamber (or a sputter), a chemical vapor deposition chamber, etc.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum, a gas plasma or other chemical environment must be provided for the wafer. For instance, in a sputter chamber, a high vacuum environment must first be provided surrounding the wafer such that metal particles sputtered from a metal target can travel to and deposit on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition chamber, a plasma cloud of a reactant gas or gases is formed over a wafer positioned in a chamber such that deposition of a chemical substance can occur on the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer therefore must be conducted in a hermetically sealed environment that is completely isolated from the atmosphere. Numerous processing equipment has been designed for such purpose. One of such widely used equipment is marketed by the Applied Materials Corporation of Santa Clara, Calif., i.e., Centura.RTM. 5000 system.
In a Centura.RTM. 5000 wafer handling system, as shown in FIG. 1, the basic system 10 consists of two independent vacuum cassette loadlocks 12 and 14, a capacity for one to four independent process chambers (two of such chambers 16 and 18 are shown in FIG. 1), a capacity for two service chambers, including the cool-down chamber 22, and a vacuum transfer chamber 20 which is isolated from vacuum cassette load locks 12, 14 and process chambers 16, 18 by slit valves 32 (shown in FIG. 3). The modular design of the basic system 10 is such that up to three high-temperature silicon deposition chambers may be used as the process chambers. The basic system 10 can be used for fully automatic high-throughput processing of wafers by utilizing a magnetically coupled robot. The basic system 10 is further capable of transferring wafers maintained at a high temperature such as 700.degree. C. The basic system 10 further allows cross-chamber pressure equalization and through-the-wall factory installation. The vacuum pumps for the process chambers 16, 18, the transfer chamber 20 and the cassette loadlocks 12, 14 are mounted at a remote location to prevent mechanical vibration from affecting the operation of the system.
Each of the vacuum cassette loadlocks 12, 14 and the process chambers 16, 18 and the service chamber 22 are bolted to the vacuum transfer chamber 20 and are self-aligned for ease of expansion or modification. Each of the process chambers 16, 18 is capable of processing a single wafer for achieving wafer-to-wafer repeatability and control. The temperatures in the process chambers 16, 18 are further closed-loop controlled for accuracy.
A plane view of the basic system 10 of FIG. 1 is shown in FIG. 2. An enlarged, perspective view of the vacuum transfer chamber 20 is further shown in FIG. 3. As shown in FIG. 3, the process chambers 16, 18 communicate with the vacuum transfer chamber 20 by slit valves 32. Similarly, the vacuum cassette loadlocks 12, 14 and the service chamber 22 (such as the cool-down chamber) communicate with the vacuum transfer chamber 20 through slit valves 32.
In the basic wafer processing system 10 shown in FIGS. 1 and 2, the handling of wafers between the various loadlock chambers 12, 14, the process chambers 16, 18 and the cool-down chamber 22 must be carefully conducted to avoid damage to the wafers. To accomplish such purpose, the wafer is handled by a wafer transfer system 24. The wafer transfer system 24, as shown in FIGS. 2, 3 and 4, consists mainly of a robotic handler which handles all wafer transfers by a single, planar, two-axis, random access, cassette-to-cassette motion. A magnetically coupled robot permits good vacuum integrity and service without interrupting chamber integrity. The major component of the wafer transfer system 24 is the quartz robot blade 28, The high-purity quartz blade 28 permits high-temperature transfer at up to 700.degree. C. without incurring contamination. A non-contact optical wafer centering process is also performed during the wafer transfer process. A constant flow of filtered inert gas such as nitrogen is used in the cassette loadlocks 12, 14 and the vacuum transfer chamber 20. An enlarged view of the wafer transfer system 24 including the quartz robot blade 28 is shown in FIG. 4. A frog-leg-type robot arm 34 is used to operate the quartz robot blade 28.
A conventional quartz robot blade 28 is shown in both a cross-sectional view in FIG. 5A and in a plane view in FIG. 5B. The robot blade 28 can be fabricated of a high temperature ceramic material such as quartz. The blade is provided with mounting holes 36 for mounting to a blade mount 38 (shown in FIG. 4). The quartz robot blade 28 normally has an elongated construction in a rectangular shape. The elongated body 40 consists of an aperture 42 provided for ventilation of the backside of a wafer (not shown), a recessed surface area 44 and three raised peripheral areas 46, 48 and 50. The first raised peripheral area 46 has a maximum diameter measured across the elongated body 40 of approximately 200 mm adapted for receiving an 8-inch wafer. The second raised peripheral area 48 acts as a cradle for holding an 8-inch wafer therein on top of the first raised peripheral area 46.
Since the robot blade 28 is fabricated of a high temperature resistant ceramic material such as quartz which has a smooth surface, problem occurs when the blade is used for transporting a silicon wafer which also has a smooth surface. The positioning of a wafer on the blade 28 resulting in two smooth surfaces being positioned face-to-face and the wafer is frequently lost by slipping off the blade during transport. When a wafer falls off the blade 28, the wafer may be either severely damaged or broken resulting in a total loss. A quartz robot blade that has a smooth top surface for engaging a wafer is therefore inadequate for transporting wafers.
It is therefore an object of the present invention to provide a wafer-transporting apparatus that does not have the drawbacks or shortcomings of the conventional wafer-transporting devices.
It is another object of the present invention to provide an apparatus for transporting semiconductor substrates which is constructed of a rectangular-shaped member that has a top surface with a surface roughness for engaging and holding a substrate thereon.
It is a further object of the present invention to provide an apparatus for transporting wafers which is equipped with a surface roughness in a top surface for engaging a wafer wherein the surface roughness is provided by a sand-blasting method.
It is another further object of the present invention to provide a wafer-transporting blade for transporting wafers into process chambers wherein the blade is fabricated of a quartz material.
It is still another object of the present invention to provide a wafer-transporting blade that is fabricated of a quartz material which has a top surface with a surface roughness formed by fusing a multiplicity of silica sand particles to the surface.
It is yet another object of the present invention to provide a wafer-transporting blade that has a surface roughness on a top surface for engaging wafers wherein the surface roughness is provided by a mechanical abrasion method.
It is still another further object of the present invention to provide a wafer-transporting blade that has a surface roughness on a top surface for engaging wafers wherein the surface roughness is provided by a chemical etching method.
It is yet another further object of the present invention to provide a method for transporting wafers to a process chamber by utilizing a wafer-transporting blade which has a surface roughness in a top surface formed mechanically or chemically such that the top surface frictionally engaging a wafer that is placed on top.